The experimental therapy, which involves the injection of a foreign gene directly into the brain, could provide a new option for those whose rigidity, tremors and other symptoms don't respond to drugs.

About a million Americans suffer from Parkinson's disease, including former Attorney General Janet Reno and actor Michael J. Fox.

The research team, headed by Matthew During, formerly at Jefferson and now associated with the University of Auckland, New Zealand, published the results of its work on rats in today's issue of Science.

During said he was trying to devise a less invasive way to duplicate the effects of another procedure, deep brain stimulation, in which doctors implant a pacemaker-like electrical device in part of the brain.

Thousands of patients around the world have been implanted with the device and some have reported significant improvements in their ability to move normally.

Scientists are still trying to understand what causes Parkinson's disease and why the implants seem to work. The hallmark of the disease is a massive die-off of neurons that normally produce the brain-signaling chemical dopamine. That happens mainly in an almond-shaped structure called the substantia nigra.

More recently, scientists have found trouble in an adjoining structure, called the subthalamic nucleus, where they see a misfiring of the neurons, creating abnormal signaling that might in turn cause more death of the dopamine-making neurons.

The implant, which goes into the subthalamic nucleus, seems to calm down the abnormal signaling, possibly shutting off a kind of feedback loop.

In the gene therapy procedure, the researchers would use surgery to inject the subthalamic nucleus with a gene that alters the inner workings of the cells, causing them to produce a chemical called GABA.

Though there is a drug, levodopa, that has helped many people, for many patients the benefits are erratic and the patients end up going from rigidity and stiffness to periods of uncontrollable movements.